CA1219963A - Shaped solder pad for surface mounting electronic devices and a surface mounting position incorporating such shaped pads - Google Patents

Shaped solder pad for surface mounting electronic devices and a surface mounting position incorporating such shaped pads

Info

Publication number
CA1219963A
CA1219963A CA000484185A CA484185A CA1219963A CA 1219963 A CA1219963 A CA 1219963A CA 000484185 A CA000484185 A CA 000484185A CA 484185 A CA484185 A CA 484185A CA 1219963 A CA1219963 A CA 1219963A
Authority
CA
Canada
Prior art keywords
mounting position
segmental
solder
outer edge
surface mounting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000484185A
Other languages
French (fr)
Inventor
Jacques Van Den Brekel
Carlyle W. Crothers
Dale B. Squires
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nortel Networks Ltd
Original Assignee
Northern Telecom Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Northern Telecom Ltd filed Critical Northern Telecom Ltd
Priority to CA000484185A priority Critical patent/CA1219963A/en
Application granted granted Critical
Publication of CA1219963A publication Critical patent/CA1219963A/en
Expired legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00Apparatus or processes for manufacturing printed circuits
    • H05K3/30Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/341Surface mounted components
    • H05K3/3431Leadless components
    • H05K3/3442Leadless components having edge contacts, e.g. leadless chip capacitors, chip carriers
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00Printed circuits
    • H05K1/02Details
    • H05K1/11Printed elements for providing electric connections to or between printed circuits
    • H05K1/111Pads for surface mounting, e.g. lay-out
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09209Shape and layout details of conductors
    • H05K2201/09372Pads and lands
    • H05K2201/0939Curved pads, e.g. semi-circular or elliptical pads or lands
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/10Details of components or other objects attached to or integrated in a printed circuit board
    • H05K2201/10613Details of electrical connections of non-printed components, e.g. special leads
    • H05K2201/10621Components characterised by their electrical contacts
    • H05K2201/10636Leadless chip, e.g. chip capacitor or resistor
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/04Soldering or other types of metallurgic bonding
    • H05K2203/048Self-alignment during soldering; Terminals, pads or shape of solder adapted therefor
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50Manufacturing or production processes characterised by the final manufactured product

Landscapes

  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Manufacturing & Machinery (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)

Abstract

A SHAPED SOLDER PAD FOR SURFACE MOUNTING ELECTRONIC DEVICES AND A
SURFACE MOUNTING POSITION INCORPORATING SUCH SHAPED PADS

Abstract of the Disclosure Solder pads for surface mounting of devices on a circuit board are given predetermined shapes. By shaping of a solder pad, or contact pad, a device will be held in, or moved to, a desired position on melting of the solder at the pad. Improved alignment and positioning is obtained. Broadly, a contact or solder pad comprises a rectangular portion and a segmental portion, the device end resting on the rectangular portion and the segmental portion being outside of the contact position.
- i -

Description

~2~
A SHAPED SOLDER PAD FOR SURFACE MOUNTING ELECTRONIC DEVICES AND A
SURFACE MOUNTING POSITION INCORPORATING SUCil SHAPED PADS

This inven-tion relates -to solder pads, for surface mounted devices, and particularly relates to a speci-Flc shaping of such pads for mounting, by reflow soldering on circuit boards. A feature of the invention is the ability to hold devices in place, an or under the surface of a circuit board, during soldering of further devices on the top surface of the circuit board.
A very large proportion of electronic devices are surface mounted on circuit boards. In such a process, a circuit pattern is deFined on a circuit board, in copper, the copper pattern being afterwards tinned, to assist soldering amongst other reasons.
Such circuit boards are generally referred to as printed circuit boards (PCB). In the circuit pattern lands are defined to which devices are to be soldered. The land sizes, and spacing, depend generally on the size of device to be mounted. Two lands may be provided for a device which is to be connected at each end. A pattern of lands may be provided for connection of leads, or contact pads, o-f encapsulated chips.
For good electrical connection it is desired that a device be centered upon the lands. Centering is also desirable to ensure satisfactory spacing of the devices. With conventional forms of circuit pattern, the contact pads for devices are usually rectangular.
Although devices may be positioned so as to be aligned correctly, and are central on the contact pads, they can move prior to soldering.
Positioning of the devices may also not be accurate and misalignment and oFf-center positioning occur. Soldering i-tself may also cause devices to move From the desirecl position.
The present invention is concerned with the spec-i-fic shaping oF contact pads. By suitable shaping oF d con-tac-t pad, a device will be held in a desired position or moved -to -the desired position if mispositioned, on mel-ting of the solder at the contac-t pad, during soldering. Substantial improvement in alignment and posi-tioning is obtained. Broadly, in accordance with the invention, a contac-t comprises a body of solder having a defined shape, the shape cornposed of a rectangular portion and a segmental portion. The rectangular portion is positioned to receive the contact member or position on the device, while the segmental portion is outside the actual posi-tion of contact. Typically for a normal device connected at each end, a pad is provided for each end, the rectangular portions oF the pads being innermost and the segmental portions being outside of the area occupied by the device. The segmental portions and rectangular portions are in alignment.
A -Further feature to which the present invention can also be applied, is the holding in position of devices on an undersurface of a circuit board, during reflow solding of further devices on the top surface of the circuit board. By providing a predetermined amount of solder, related to the weight of the device, the device will stay in position on the undersurface even though the solder attaching it is molten, The invention will be readily understood by the following description of certain embodiments, by way of example, in conjunction with the accompanying diagrammatic drawings, in which:-Figure 1 is an illustration of a device;
Figure 2 is an illustration of a mounting position -for a device as in Figure l; and Figure 3 illustrates an individual pad with the segmental por-tion parameters~
Figure 1 illustrates a typical electronic device or component lO, which is rectangular in plan form, usudlly elongate, and is usually rectangular in cross-section viewed from an end. Each end of the device is "tinned" at 11, to assist in soldering.
Figure 2 illustrates a typical mounting position having two contact pads 12 spaced apart, the device or component indicated in dotted outline at 10. Each pad comprises a rectangular portion 13 and a segmental portion 14. The rectangular portions and the segmental portions are aligned, with the segmental portions being on the outside of the rectangular portions in relation to the position. The tinned contact portions or ends 11 of the device are positioned on the rectangular portions 13.
Figure 3 illustrates a single pad, with the rectangular portion 13 and segmental portion 14, joining at the chain dotted line 15. The shape of the segmental portion 14 can vary to some extent.
The outer edge 16 of the segmental portion is defined by a curve which, preferably is a parabolaO A semi-circle will be quite effective but, particularly for relatively large contact pads, occupies more space than a parabola. Also, preferably, the ends of the curved edge 16 and the side edges 17 of the contact pad blend smoothly, the side edges being tangential to the curve. ~owever, this is not essential and is sometimes difficult to obtain in manufacture.

~L2~9~i3 The action of the segmental portion is to centralize the end of the device or component. The process for mounting of components is generally as follows~ al-though variations in the speciFic process can occur:-1. The circui-t board has a circui-t pat-tern de-F-ined on one or both sur-faces - this is done by conventional means, such as by photolithographic etching;
2. The circuit pattern - generally of copper - is tin plated, this can comprise several steps including a thin copper plating before tin plating7 and is conventional;
3. Solder paste is applied, as by screen printing or other conventional methodj
4. The solder paste is melted, as by heating the circuit board in a vapour at fusion temperature - generally referred to as reFlow soldering - a conventional step or process.
After step 4, the circuit board has a plurality of solder pads each of which is generally of the form as in Figure 3, usually arranged in pairs, as in Figure 2, but also arranged in a row of pairs or in some other pattern. A device is then positioned on the circuit board at each desired position. The actual size of the individual solder pads varies with the size of the device, as described later, The devices are kept in place by the application of a flux to the solder pads prior to positioning of the devices, the flux acting as an adhesive.
The circuit board is then again heated, to melt the solder of the solder pads. Once the solder has melted, then the shape of a pad acts to pull the related end, or contact point, of the device 36~
into a central position. This occurs from the effect of -the segment of solder in the segmental portion 14. The segment, when molten, because of surface tension, tends to move the related end of the device into alignment with the cen-ter or focus -f o-f the segmen-tal portion, The center, or focus, is generally on or close to the junction between the rectangular portion and the segmental portion, that is line 15. The rectangular portion 13 also takes a part in the posi-tioning of the end of the device. Once the solder on this portion is molten it tends to center the device on the center line of the rectangular portion. By having a segmental portion 14 at each end, when they are molten, they also tend to centralize the device, end-to-end, on the two pads. This again occurs because of the surface tension in the molten solder at the segments. The surface tension will be equalized when the longitudinal positioning of the device is symmetrical relative to the focus of each segmental portion.
Figure 3 indicates some basis parameters for the segment. The curve of the outer edge is defined by the equation Y = ~ ~F
where Y is a point on the curve and X and P are distances from the junction line 15 and the distance from an axis normal to the line 15 respectively. Various other parameters apply. Thus, considering Fi~ure 2, in conjunction with Figure 1, the distance over the rectangular portions 13 - E in Figure 2 - is generally equal to the overall length of the device - A in Figure 1 - plus from approximately .02 inches to about .03 inches. The width of the pads, that is the width of rectangular portion 12 - D in Figure 2 - is generally equal to the width of the device - C in Figure 1 - plus an amoun-t of from about i3 .02 inches`to about .04 inches, the actual amount increasing with the width of the device. The length of the rectangular portion of a pad -F in Figure 2 - is equal to the length of the tinned portion of the device - B in Figure l - plus about .01 inches. These parameters can vary slightly, and will also be affected slightly by the size of the device~ For very small devices, the segmental portion essentially becomes a segment of a circle, while for longer devices it is or approaches a segment of a parabola, which reduces the overall length.
The overall length - G in Figure 2 - is determined by E and the effect of the curve or parabola 16. As this curve 16 is dependent to at least some extent on the width C of the device, the length G will thus also be dependent to some extent on the component width. As stated previously, while ideally the curve should blend smoothly with the side of the rectangular portion 13, the side being tangential to the curve, this is not essential, the curve sometimes taking the shape indicated by a dotted line 17 in Figure 2.
A further feature of the invention is the ability to hold devices in position while the board is reversed, that is with surface mounted devices on the undersurface, while reFlow soldering further devices on the top surFace. The devices on the bottom surface are held in place, even though the solder is molten.
A typical range of dimensions related to component size is as follows:-COMPONENT NUMBER
1812 18?5 1206 0805 A .180 .18 .12 .08 C .12 .25 .060 .05 D ~ .16 o28 ~09 ~07 E _ .21 .21 .15 .11 F ~ .0~0 .07 .02 .015

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A solder mounting position for an electronic device adapted to be mounted on a substrate surface, comprising at least one pair of solder pads spaced apart along a horizontal axis, each solder pad of substantially uniform thickness and having a rectangular portion with inner and outer edges and an arcuate segmental portion extending from said outer edge of the rectangular portion along said horizontal axis, the inner edges of the rectangular portions being in opposition and the segmental portions extending outward away from each other;
each rectangular portion having a width, measured in a direction normal to said axis, approximately equal to the width of the device plus an amount varying from about .02 inches to about .04 inches, the amount increasing with increasing width of the device;
each segmental portion having a straight inner edge contiguous with the outer edge of the rectangular portion, and a convex curved outer edge joining at each end to the ends of said inner edge of the rectangular portion.
2. A mounting position as claimed in claim 1, the length of each rectangular portion, in the direction of said axis, being approximately equal to the turned length at an end of the device plus about .01 inches.
3. A mounting position as claimed in claim 1, the curved outer edge of each segmental portion approximating to a segment of a circle.
4. A mounting position as claimed in claim 3, the curved outer edge of each segmental portion approximating to a semi-circle.
5. A mounting position as claimed in claim 1, the curved outer edge of each segmental portion approximating a segment of a parabola.
6. A mounting position as claimed in claim 1, the curve of each outer edge of the segmental portions being defined by where Y is a point on the curve and X and P are, respectively, distances from said straight inner edge and from said axis.
7. A mounting position as claimed in claim 1, including a plurality of said pairs of solder pads, the axes being parallel.
8. A mounting position as claimed in claim 7, said pairs being aligned in a direction normal to said axes.
CA000484185A 1985-06-17 1985-06-17 Shaped solder pad for surface mounting electronic devices and a surface mounting position incorporating such shaped pads Expired CA1219963A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA000484185A CA1219963A (en) 1985-06-17 1985-06-17 Shaped solder pad for surface mounting electronic devices and a surface mounting position incorporating such shaped pads

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA000484185A CA1219963A (en) 1985-06-17 1985-06-17 Shaped solder pad for surface mounting electronic devices and a surface mounting position incorporating such shaped pads

Publications (1)

Publication Number Publication Date
CA1219963A true CA1219963A (en) 1987-03-31

Family

ID=4130722

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000484185A Expired CA1219963A (en) 1985-06-17 1985-06-17 Shaped solder pad for surface mounting electronic devices and a surface mounting position incorporating such shaped pads

Country Status (1)

Country Link
CA (1) CA1219963A (en)

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